This invention relates generally to a stimulated brillouin scattering (SBS) cell for use in a laser system and, more particularly, to an SBS cell for use in a solid state laser system, where the SBS cell includes concentric inner and outer tubes filled with a cell fluid and where the position of the fill hole for the inner tube prevents air bubbles from entering the inner tube.
1. Field of the Invention
This invention relates generally to a stimulated brelloulian scattering (SBS) cell for use in a laser system and, more particularly, to an SBS cell for use in a solid state laser system, where the SBS cell includes concentric inner and outer tubes filled with a cell fluid and where the position of the fill hole for the inner tube prevents air bubbles from entering the inner tube.
2. Discussion of the Related Art
Certain laser systems employ a stimulated brillouin scattering (SBS) cell that is used to provide beam waterfront cancellations to correct for optical distortions. The SBS cell is positioned within the laser system so that the laser beam is first directed through the cell, and this is reflected back through the cell by a reflector. The SBS cell is filled with a fluorinated cell fluid that provides a certain desirable phase conjugation optical interaction with the beam. This phase conjugation provides auto-alignment, significantly relaxes stability requirements of the laser optics, and provides wavefront cancellation to correct optical distortions. The operation of an SBS cell of this type is well understood to those skilled in the art.
The SBS cell must include an air cavity to operate effectively. Air trapped within the SBS cell provides a compressible volume that the fluid can expand into as temperature increases. Vibrations and acoustical loads within the cell cause the air and cell fluid to mix which generates air bubbles that induce a refractive index gradient within the fluid. If the bubbles in the fluid are in the path of the beam, the refractive index gradient compromises the auto-alignment and wavefront distortion properties of the fluid, which may lead to laser breakdown during operation. Therefore, it is necessary that the laser be operated under minimal vibrations, or suitable damping be provided to prevent agitation of the cell. Additionally, the SBS cell must isolate the fluid from thermal gradients that may also act to induce refractive index gradients. This can also lead to laser breakdown during operation.
Airborne laser illuminator systems are known in the art that are mounted on aircraft for target detection and tracking purposes. During normal flight conditions, the SBS cell associated with such laser systems may be subjected to significant vibration and acoustical loads, as well as temperature variations, as a result of normal flight conditions. Currently available damping systems that may be applicable for vibration damping for a ground based system are ineffective in this environment.
What is needed is a modified SBS cell that prevents air pockets, fluid distortions and the like from affecting the cell fluid under normal operating conditions. It is therefore an objection of the present invention to provide such an SBS cell.
In accordance with the teachings of the present invention, an SBS cell is disclosed for use in combination with a laser system on a mobile platform. The SBS cell includes concentric inner and outer tubes that define concentric inner and outer chambers, where the laser beam propagates down the inner chamber. The inner tube is completely filled with an SBS fluid and the outer tube is filled to a level that is above the fill hole of the inner tube. The outer tube is sized to trap enough air to provide a suitable compressible volume for cell fluid expansion resulting from temperature changes in the laser environment. The SBS cell is filled in an upside-down position, and the cell is then rotated 180 degrees to its operating position. In the operating position, the fill hole is pointed downward, and since the air bubbles will float to the top, the distance from the inner tube fill hole and the trapped air bubbles is sufficient enough to prevent air bubbles from migrating to the fill hole and entering the inner tube. Without air bubbles within the inner tube, the sloshing of the fluid within the cell from vibrations does not create an index of refraction gradient in the inner tube that would affect the optical beam.
Additional objects, advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.